Triggered pulse generator



Sept. 29, 1959 E. c. 1.. D; FAYMOREAU EI'AL 2,906,374

TRIGGERED PULSE GENERATOR Fiied June 5. 1956 AN00 6 OFF INVENTORS 51154015 05 F4 rmkiw MARK MANOL A ORNEY United States Patent ()fitice 2,906,874 Patented Sept. 29, 19,59

TRIGGERED PULSE GENERATOR Etienne C. L. de Faymoreau, Nntley, and Mark Mandel, Bloomfield, N.J., assignors to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland Application June 5, 1956, Serial No. 589,500

Claims. (Cl. 250-27) This invention relates to triggered pulse generators, particularly to those generally referred to as monostable multivibrators.

Monostable multivibrators consist essentially of two tubes one of which is normally conducting and the other of which is blocked. For example, the first tube may be the normally conducting tube, and the second tube may be normally blocked. In response to an input trigger pulse (negative), the first tube is momentarily blocked, and the second tube conducts. This state continues for a given period at the end of which the first tube will again conduct and the second tube will be blocked. The width of the pulse produced by such a multivibrator is principally determined by the constants of an R-C circuit. However, assuming that the triggering pulse is of greater width or duration than the duration of a complete vibration of the multivibrator, the input pulse will vary the bias level of the first tube and change the point of time at which it will begin conducting, thereby affecting the period of vibration or width of the output pulse. In many instances, it is desired that this pulse width be constant and unaffected by the duration of the triggering pulse. A typical example of this is in certain searching and tracking arrangements, such as in the aerial navigation system known as Tacan, in which continuously phaseshifted triggering pulses are applied to a monostable multivibrator to produce gating pulses, which gating pulses are likewise shifted in time until a reference pulse is coincidental therewith, the phase shift at which coincidence of the reference pulse with the gate occurs being an indication of a given sector of azimuth with respect to a beacon station. If the gating pulse is too wide, an improper indication will occur, and the wrong sector will be indicated. It is, therefore, essential that the gate have a fixed width. The triggering pulses are derived from a slow wave and have a greater width than the width of the gating pulses. It is, therefore, important in this system that once the monostable multivibrator has been triggered its resultant pulse width is determined by the RC constants of the multivibrator and not by the width of the triggering pulse.

It is also desirable that some of the transients produced in the circuit While the monostable multivibrator is generating a pulse should not appear in the output, such as, for example, tails attached to the output pulse, for these could produce a false operation.

An object of the present invention is the provision of an improved trigger circuit of the type hereinbefore de scribed.

Another object of the present invention is the provision of a monostable type of multivibrator in which the duration of the output pulse produced is independent of the duration of the triggering pulse applied.

A further object of the present invention is the provision of such a triggered pulse generator in which the output tube also serves as a threshold device to only permit an output above a given threshold level.

Other and further objects of the present invention will become apparent and the foregoing will be better understood with reference to the following description of an embodiment thereof, reference being had to the drawings, in which:

Fig. 1 is a schematic diagram of a trigger circuit of the monostable-multivibrator type; and

Fig. 2 is a set of curves used in explaining the operation of the circuit of Fig. 1.

Referring now to Fig. l, the circuit there disclosed includes two tubes consisting of a pentode 1 and a triode 2. An input pulse is applied over line 3 and across a resistor 4 to the suppressor or third grid 5 of tube 1. The anode 6 of tube 1 is coupled to the grid 7 of tube 2 via capacitor 8 while the anode 9 of tube 2 is coupled to the control or first grid 10 of tube 1 via capacitor 11. The screen 01' second grid 12 of tube 1 is connected via a resistor 13 and via capacitor 8 to the grid 7 of tube 2. Anodes 6 and 9 are connected via anode resistors 14 and 15, re spectively, to the positive side of a source of anode potential 16. to ground 18, a common point of reference potential, while the cathode 19 of tube 2 is connected via a cathode resistor 20 to ground. The cathode 19 is also connected via resistor 21 to the positive-potential source 16. The output is taken from an output terminal 22 likewise. connected to the cathode 19 of tube 2. The control grid 10 is connected via a tapped variable resistor 23 having a tap 24 to the positive-potential source 16. The tap 24 is connected via a resistor 25 to one contact 26 of a switch 27 which may be a relay, the switch arm making contact with contact 26 being connected to ground 18.

The operation of this circuit may be described as follows. Normally, that is, in the absence of any triggering pulses, tube 1 conducts, and tube '2 is blocked. Tube 1 conducts because its control grid 10 and screen grid 12 are connected via resistor 23 and resistors 13 and 14, respectively, to the positive-potential source 16 while tube 2 is blocked because its cathode 19 is connected to the same source 16 by voltage-dividing series resistors 20 and 21.

When a negative input pulse is applied over input line 3 to the suppressor grid 5 of tube 1, it lowers the current to the anode 6, thereby raising the potential thereof and applying a positive voltage to grid 7 of tube 2 causing said tube to conduct. The anode 9 of tube 2 starts to go negative; and this negative voltage is fed back to the control grid 10 of tube 1, further lowering the current flow in tube 1 and raising the voltage of anode 6. This action is triggerlike or cumulative'so that tube I quickly becomes cutoff while the conduction of tube 2 rises rapidly to a maximum. The rapidly rising current through tube '2 produces a rapidly rising voltage on the, cathode 19 which appears at the output 22 as the leading edge 28 of the output pulse 29, as shown in Fig. 2. The negative input pulse 30 is likewise depicted in Fig. 2. After tube 2 reaches its maximum conductivity, it remains substantially at this level as indicated by the flat portion 31 of the output pulse. During this period, condenser 11 discharges through resistor 23, thereby lowering the negative bias on grid 10 of tube 1 until it reaches a level at which electron current starts to flow from cathode 17 to the screen grid 12. Screen grid 12, becoming more negative,

. in the trailing edge 32 of the output pulse as the conductivity of tube 2 is rapidly lowered. It will be recog nized that this action occurs despite the fact that the input pulse 30 is of greater width than the output pulse 29 and The cathode 17 of tube 1 is connected despite the fact that the input pulse still prevents current from flowing to the anode 6 of tube 1. Tube 2, however, will not be entirely cut off as indicated by line 33 until the input pulse has terminated. However, the cathode resistor 20 develops a biasing voltage indicated by the dotted line 34 during the conduction of tube 2, which forms a threshold level so that no output is produced at point 22 unless it is above said level. Thus, the resultant output is that portion of pulse 29 indicated by crosshatching.

As is apparent from the foregoing discussion, the width of pulse 29 is determined by the capacity of condenser 11 as well as the resistance of resistor 23. In certain operations, such as in tracking and searching, where the output pulse is used to capture a reference pulse, it is frequently desirable to change the width of the output gating pulse so that it will be narrower at one time so as not to pick up a false reference pulse or two reference pulses. When this is desired, the relay 27 is operated, causing contact 26 to be connected to ground and thereby shorting out the portion of resistor 23 above the tap point 24. This results in a narrowing of the output pulse produced, which depends upon the position of tap 24, and may narrow output pulse 29 as indicated by the dotted line 35.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. A triggered monostable multivibrator for generating rectangular pulses of constant width comprising a pair of electron discharge devices each having a cathode, anode and a control electrode, the first of said devices having, in addition, second and third control electrodes spaced consecutively from said cathode after its first control electrode, a capacitor coupling the anode of said first device to the control electrode of the second device, second means coupling the anode of said second device to the first control electrode of the first device, said second means including a time constant network which controls the duration of the output pulse produced by the generator, means coupling said second control electrode of said first device to said control electrode of said second device, a source of positive potential connected via the resistance of said network to the first control electrode of the first device for biasing said first device to normally conduct, means biasing said second device to normally block conduction of said second device and means for applying input pulses to said third control electrode of said first device for triggering said pulse generator.

2. A triggered monostable multivibrator for generating rectangular pulses of constant width according to claim 1, wherein said means for biasing said second device includes means for connnecting said source of positive potential to the cathode of said second device.

3. A triggered monostable multivibrator for generating rectangular pulses of constant width according to claim 1, further including a resistor in series with the cathode of said second device and an output connection taken between said cathode and said resistor for deriving rectangular pulses of constant width irrespective of the duration of a triggering pulse input.

4. A triggered monostable multivibrator for generating rectangular pulses of constant width comprising a pair of electron discharge devices each having a cathode, anode and a control electrode, the first of said devices having, in addition, second and third control electrodes spaced consecutively from said cathode after its first control electrode, means for biasing the first control electrode of said first device to render it normally conducting, means for biasing said second device to render it normally nonconducting, cross coupling means comprising two capacitance resistance circuits for connecting a pair of control electrodes of the first device to the anode of the second device, the capacitance of one of said latter circuits being coupled between the anode of the first device and the control electrode of said second device, means for applying triggering pulses to the third control electrode of the first device to block conduction thereof causing said second device to conduct, the change in the electrical condition of the time constant network after a predetermined time causing current to flow from the cathode of said first device to the second control electrode thereof, and means comprising a resistor coupling said second control electrode to the control electrode of said second device to apply the negative voltage developed on said second control electrode to the control electrode of said second device to lower conduction thereof.

5. A triggered monostable multivibrator for generatingrectangular pulses of constant width according to claim 4, further including a resistor in series with the cathode of said second device and an output connection taken between said cathode and said resistor, the current through said resistor producing a bias establishing a threshold level for the output of said second device.

References Cited in the file of this patent UNITED STATES PATENTS 2,505,542 Hahn Apr. 25, 1950 2,530,931 Alexander Nov. 21, 1950 2,556,934 Mulligan et al June 12, 1951 2,743,364 Kraft Apr. 24, 1956 2,789,225 Fleming Apr. 16, 1957 

